Generally, such an electric motor having a speed reduction mechanism includes an electric motor and a speed reduction mechanism that decelerates rotational speed of the electric motor, as is disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 8-275441. The speed reduction mechanism includes a case frame having housed therein a worm deceleration mechanism and a bearing for supporting a motor shaft, and a case cover that is attached to the case frame along the direction of the motor shaft. The case frame has a brush holder fixed thereto, in which a brush that slidably comes into contact with a commutator of the electric motor is housed. The brush holder is provided with brush side terminals to be electrically connected to the brush. On the other hand, the case cover is provided with power side terminals to be electrically connected to a lead wire for supplying power. These brush side terminals and power side terminals are arranged above the motor shaft. When the case cover is fixed to the case frame, these terminals are coupled to each other to electrically connect the power-supplying lead wire and the brush.
On the other hand, since the electric motor having a speed reduction mechanism has these terminals arranged above its motor shaft, the size above the motor shaft is increased by the size of these terminals, which undesirably increases the thickness of the electric motor. So as to reduce the size and thickness of the electric motor, the position of these terminals is shifted from above the motor shaft to laterally next to the motor shaft, thereby reducing the size above the motor shaft. FIGS. 13(a) and 13(b) show explanatory diagrams for explaining the conventional electric motors having speed reduction mechanism. FIG. 13(a) shows an electric motor of a center connecting type in which terminals 51 are arranged above a motor shaft 52, while FIG. 13(b) shows an electric motor of a side connecting type in which the terminals 51 are arranged laterally next to the motor shaft 52. As is apparent from FIG. 13, when the arrangement of the terminals 51 is changed from the center connecting to the side connecting type, the electric motor has its thickness reduced by the size of these terminals (that is, the thickness of the electric motor is reduced from T1 to T2).
However, there are an electric motor having speed reduction mechanism of a right side terminal type and that of a left side terminal type due to the condition of designing, which are under the relationship similar to the case of an image and its mirrored image, as shown in FIGS. 14(a), 14(b). Thus, if the terminals 51 are of a side connecting type shown in FIG. 13(b), right side specification and left side specification are necessary for not only case frames and case covers but also brush holders provided with brush side terminals. That is, parts of the same kind have to be manufactured for the respective specifications, which undesirably increase the kind of parts. Furthermore, dies have to be prepared individually, which undesirably increases the manufacturing cost.
Accordingly, the present invention has an object to share a brush holder in electric motors having a speed reduction mechanism which are of different specifications so as to reduce the manufacturing cost.